On immigration reform, the two front-runners argued for nearly twelve minutes.

Gingrich claimed that Romney would heartlessly deport people who've been here a long time.

But Romney says it's about the law, that he wants strict hiring guidelines that would prevent undocumented workers from getting jobs, and therefore, force them to self-deport.

"To use that rhetoric, suggests to people that somehow, if you're not willing to keep people here who have violated the law, that you're anti-immigrant. Nothing could be further from the truth," said Romney.

Gingrich wants a path to residency for those who've been here for decades and who have followed the law.

"So that he or she can finish their life with dignity, within the law," said Gingrich.

The battle comes as Romney has regained a small lead in statewide polling over Gingrich.

Both candidates have worked to court Hispanic voters in Florida, who make up eleven percent of Republicans.

But Florida's housing crisis was also a central theme.

Gingrich tried to beat back a common Romney theme that Gingrich made money as a consultant for government mortgage lender Freddie Mac while they were doling out mortgages that weren't repaid.

"I'd had about enough of this. We discovered to our shock that Gov. Romney owns shares of both Fannie Mae and Freddie Mac. Governor Romney made a million dollars off of selling some of that," said Gingrich.

"First of all, my investments aren't made by me, they're in a blind trust," responded Romney.

Needing a strong showing to try to blunt Gingrich's harsh attacks of recent days, Romney was forceful and had the former House speaker on his heels on some issues.

At the same time, Rick Santorum had his strongest debate performance so far, coming across as a sincere and committed candidate who would best represent conservative principles.

In the final debate before the primary, Santorum returned to a familiar attack over health care, in hopes it would drag the front-runner down.

"Your mandate is no different than Barack Obama's mandate. It is the same mandate," said Santorum.

"Romney won two ways tonight," said CNN contributor and Republican strategist Alex Castellanos. "One, by having a good debate and two by having Santorum have his best debate yet."

Romney appeals to the more moderate wing of the Republican Party while Santorum and Gingrich are competing for the conservative vote. If Santorum can build support, it would hurt Gingrich as the primary process continues.

Ron Paul also had a good night, repeatedly prompting laughter and applause with self-deprecating one-liners and clear messaging about his libertarian policies that excite young supporters.

The Republican Party of Florida expects more than two million Republicans to vote on Tuesday.

Rachel Streitfeld and Adam Aigner-Treworgy of CNN contributed to this report

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